1. Field of the Invention
The present invention relates to a mobile communication device, and particularly to a power supply for a mobile communication device carrying out wireless data communication.
2. Description of the Related Art
Conventionally, in a mobile communication device such as a portable telephone and a car telephone, during communication to a base station, when a battery voltage becomes lower than a voltage necessary for the communication, the communication is cut off. Thus, after exchanging a battery, a user of the communication device must make operations again for connection of a communication line, such as a calling operation. Besides, since various kinds of information required for communication operations or for signal processing are stored in a RAM, they are lost at the exchange of the battery.
With regard to such a problem, for example, Japanese patent application Laid-open No. Hei. 5-22188 discloses a technique in which when a battery voltage is lowered, data stored in a RAM is stored in an EEPROM to protect the data.
FIG. 1 is a structural block diagram schematically showing a mobile communication device disclosed in the publication.
In FIG. 1, at the reception of a signal from a not-shown base station, the signal received through an antenna 51 is subjected to processing such as amplification and demodulation by a wireless section 52. Thereafter, the output of the wireless section is subjected to predetermined signal processing by a signal processing section 53 and is outputted as a voice from a speaker 54.
On the other hand, when a signal is transmitted to the base station, a line is connected by the operation of a key pad 60. Thereafter, a voice from a microphone 55 is subjected to predetermined signal processing by the signal processing section 53, and then, is subjected to processing of demodulation and amplification and is transmitted from the antenna 51.
A micro-computer (hereinafter referred to as a microcomputer) 56 is a circuit for controlling and processing these transmitting/receiving operations, and the information regarding the controlling or processing is stored in a RAM 57.
A battery 62 supplies power to the respective sections of the communication device, and the output voltage thereof is monitored by a voltage monitoring circuit 61. On the basis of the output of the voltage monitoring circuit 61, when the battery voltage becomes lower than a predetermined value, the microcomputer 56 stores the information stored in the RAM 57 into an EEPROM 58. In this way, the information is protected.
Thereafter, after an exchange of batteries is ended, the information stored in the EEPROM 58 is restored in the RAM 57, and on the basis of the information from the RAM 57, the microcomputer 56 makes setting of a transmission/reception channel, transmission/reception output level, and the like. That is, the state before the power was cut off is recovered. Then the operation of the device shifts to a communication operation.
On the other hand, in recent years, wireless communication of data from an information terminal such as a personal computer is carried out by using a mobile communication device. It is also possible to use the above described mobile communication device in this wireless data communication.
However, in the above described conventional mobile communication device, when a drop in battery voltage is detected, the information must be transmitted from the RAM to the EEPROM, and the information must be recovered from the EEPROM to the RAM after the exchange of batteries is ended.
On the other hand, even if the above described conventional mobile communication device is applied to the wireless data communication, data from the information terminal is lost by the voltage drop of the mobile communication device. Otherwise, it is necessary to interrupt the data communication by a communication application which has operated until now at the side of the information terminal. Thus, if the application at the side of the information terminal does not retransmit all the data lost during the interruption, data communication after resumption can not be realized. That is, the data communication which has been carried out by the communication application at the side of the information terminal comes to nothing, and the same data communication must be carried out again, so that finite radio frequencies are wasted, and also time is wasted.